1. Field of the Invention
The present invention relates to a selector valve device, more particularly a selector valve device that controls the opening and closing of a fluid passageway in response to both an input current signal and the ambient temperature. The device of the present invention is especially used for an apparatus such as a so-called carbureter outer vent controller to prevent the evaporated fuel gas generated in the carbureter float chamber of an automobile engine from being discharged into the atmospheric air.
2. Prior Art
One of the conventional devices of this type is disclosed, for example, in the Japanese Laid-open Patent Publication No. 60382/1985 (Toku-kai-sho 60-60382), which is shown in FIG. 3. This conventional device is equipped with an electromagnetic mechanism including outer periphery yoke 40 comprising a magnetic material fixed to the right side end of body 31, inner core 43 disposed on the center axis in the outer periphery yoke, bobbin 44 made of non-magnetic material inserted and fixed to the outer periphery of the inner core 43, solenoid coil 47 wound on said bobbin, plunger 49 disposed movably in the axial direction facing said core on the same axis of the aforementioned inner core 43, and shaft 51, one end of which is fixed to said plunger and the other end is disposed facing the valve body 36; and a temperature sensing mechanism including first spring 37 for biasing the valve body 36 in the direction of closing the valve, and second spring made of shape memory alloy and stretchable to the memorized shape at a high temperature to bias valve body 36 in the direction of opening the valve through the shaft. When the ignition switch is turned on, solenoid coil 47 is excited regardless of the temperature change in the carbureter float chamber, plunger 49 is drawn to inner core 43, shaft 51 fixed to said plunger 49 compresses second spring 54 to move rightward in the figure, and disengages from valve body 36, so that said valve body 36 is brought into contact with sheet member 38 by the biasing force of first spring 37 so as to shut off communication between inlet port 32 and outlet port 33.
When the ignition switch is turned off and the carbureter float chamber is at a high temperature (higher than 50.degree. C.), second spring 54 made of shape memory alloy expands to the memorized shape and biases valve body 36 in the direction of opening the valve through the shaft. Here, the load is set at a larger value than that of first spring 37, so that valve body 36 disengages from sheet member 38 and inlet port 32 and outlet port 33 communicate with each other.
When the carbureter float chamber is at a low temperature, valve body 36 and, through valve body 36, shaft 51 and plunger 49 shrink second spring 54 by the biasing force of first spring 37 shown at the right in the figure, of which load is set at a larger value than that of second spring 54, and the valve body is moved until it comes into contact with sheet member 38. Thus the communication between inlet port 32 and outlet port 33 is shut off.
In the conventional device in FIG. 3 described above, when the ignition switch is turned off, there is a difference between the temperature in the carbureter float chamber to control the opening and closing of the valve body and the ambient temperature which expands the second spring made of shape memory alloy and which actually controls the opening and closing of the valve body when the valve body moves between the valve opening position and the valve closing position because of the temperature change in the carbureter float chamber. Consequently, the carbureter outer vent device does not operate because the ambient temperature of the second spring is lower than the set temperature though the temperature in the carburetor float chamber is higher than the set temperature of the changeover valve, resulting in the problem that the restarting capability of the engine at high temperature deteriorates.